In performing an injection molding operation using a new mold mounted in an injection molding machine for the first time, it is necessary to obtain a molding condition for stably obtaining a conforming product by performing a condition setting operation to adjust various items of the molding condition, i.e. temperature of an injection cylinder, injection pressure, injection speed, injection/pressure-holding switching position, screw back position, etc. There is a molding condition item such as the screw back position with regard to measurement, in which precise setting data can be obtained by a calculation process based on the weight of a product molded in an over-packed condition, specific gravity of molding material and a diameter of an injection screw, etc. However, most of the molding conditions such as cylinder temperature, injection pressure, injection speed, injection/pressure-holding switching position are ordinarily set by an operator on the basis of his or her experiments. As a result, it is difficult to appropriately set these molding condition items except by a very skilled operator. It is also inevitable to repeat the setting operation by on a trial-and-error basis to obtain the appropriate molding conditions.
However, even if the molding condition is obtained by the complicated operation as an appropriate molding condition, a stable product is not always consistently obtained and instances in which a non-conforming product is produced may occur. Of course, there is an apparent cause such as a temperature variation in the atmosphere, but other unobvious phenomenons such as an accumulation of errors caused by inappropriate molding conditions which have not appeared in the initial state, a mold temperature not reaching a balanced state, or a viscose resistance of lubricated parts of the injection molding machine varying with time, may cause an abnormality of molding. Most of the modern injection molding machines are designed to carry out feedback controls with respect to injection pressure, injection speed and temperature of the injection cylinder, but the aforementioned unobvious phenomenons are not overcome by such a control process and an abnormality which has been suppressed by feedback control at an initial stage may suddenly appear at a stage at which the ability of the machine to adapt is exceeded. The causes of these phenomenon are not clear and raise a problem in the molding operation.
Thus, in order to obtain a molding condition for producing a stable product for a long time, it is inevitably necessary to modify the molding condition which has been obtained as appropriate in the initial stage and to repeatedly carry out a considerable number of test shots under the modified condition to obtain data to confirm stability, and to select the molding condition to be appropriate from the results. Of course, an operator is required to perform a modification operation of the molding condition in constant attendance on the injection molding machine until the test shots are completed. It is not appropriate for the operator to do such operation for a long time in view of a running cost and in many cases the molding condition is determined on compromise and it is not assured that the molding operation is carried out under the appropriate molding condition.